The news that atmospheric concentrations of carbon dioxide, the most important global warming gas, have hit 400 parts per million for the first time in millions of years increases the pressure on President Obama to deliver on his pledges to limit this country's greenhouse gas emissions.
America cannot solve a global problem by itself. But as Mr. Obama rightly observed in his inaugural address, the United States, as both major polluter and world leader, has a deep obligation to help shield the international community from rising sea levels, floods, droughts and other devastating consequences of a warming planet. In his State of the Union speech, he promised to take executive action if Congress failed to pass climate legislation.
Which is just what he will have to do. The prospects for broad-based Congressional action putting a price on carbon emissions are nil. The House is run by people who care little for environmental issues generally, and Senate Republicans who once favored a pricing strategy, like John McCain and Lindsey Graham, have long since slunk away. Meanwhile, Republicans on the Senate Environment and Public Works Committee have spent the last two weeks trying to derail Mr. Obama's nominee to run the Environmental Protection Agency — a moderate named Gina McCarthy. Ms. McCarthy has served two Republican governors (Mitt Romney was one) but is considered suspect by the right wing because she wants to control carbon pollution, which is driving global temperatures upward.
Hence the need for executive action. Yet we are now four months into Mr. Obama's second term, and there is no visible sign of a coherent strategy. One plausible reason is that Mr. Obama has been preoccupied with other issues and that his key players on climate have not been in place. But that excuse disappears if Ms. McCarthy can survive a threatened Senate filibuster; even if she does not, Mr. Obama has sufficient talent in the E.P.A. and the Energy Department and among his science advisers to get started.
As this page has noted, it is possible to adopt a robust climate strategy based largely on executive actions. The most important of these is to invoke the E.P.A.'s authority under the Clean Air Act to limit pollution from stationary industrial sources, chiefly the power plants that account for almost 40 percent of the country's carbon emissions. The agency is reworking a proposed rule to limit emissions from new power plants. A more complex but no less necessary task is to devise rules for existing power plants, which cannot be quickly shuttered without endangering the country's power supply, but which can be made more efficient or phased out over time.
Mr. Obama can also order the E.P.A. to curb the enormous leakage of methane, a potent global warming agent, from gas wells and the pipes that bring natural gas to consumers. This is critical if America's bountiful supplies of cheap natural gas are to become a cleaner bridge from coal to alternative energy sources like wind and solar power.
He can hasten the development of less-polluting alternatives to older-generation refrigerants and other chemicals. He can order the Energy Department to embark on a major program to improve the efficiency of appliances and commercial and residential buildings, which consume a huge chunk of the country's energy supply. And he can ramp up investment in basic research.
All of this will take time, which is why it is important to get started. The most important of Mr. Obama's first-term environmental initiatives — the historic fuel economy standards that will double the efficiency of America's cars and light trucks — took more than three years to complete between the time they were proposed and when they were finalized last August. New power plant standards can be expected to take at least as long.
Mr. Obama has a firm grasp of the climate issue, and no one doubts that he cares about it. But as is often the case with this president, the question is whether he will exhibit a sense of urgency to match his intellectual understanding.